Get rid of Unicode::UTF8 as dependency

[jhthorsen]

Is your feature request related to a problem? Please describe.
Unicode::UTF8 require "make", which makes (no pun intended) it harder to install Convos.

Describe the solution you'd like
I think the solution can be found in jhthorsen/mojo-irc#11.

Describe alternatives you've considered
An alternative could be just removing special unicode handling all together, since maybe not too many use latin anymore..?

[jhthorsen]

The problem I'm facing is to write a test that both generates unicode and latin input and checks that only unicode is indeed returned.

[jhthorsen]

Even though I personally really want to fix this, I'm going to put it in the fridge for now 😞